Catalysts containing copper and zinc for the purification of ethylene

ABSTRACT

Catalysts for the purification of ethylene comprising copper and zinc and, if desired, one or more promoters and supports are produced by precipitation, drying, calcination and pressing, with or without addition of additives, and the pressed catalyst particles are subjected to further calcination at from 300 to 700° C.

[0001] The present invention relates to catalysts for the purificationof ethylene comprising copper and zinc and, if desired, one or morepromoters and supports and produced by precipitation, drying,calcination and pressing, with or without addition of additives, whereinthe pressed catalyst particles are subjected to further calcination atfrom 300 to 700° C.

[0002] Ethylene is an important raw material for the production ofpolyethylene. The industrial-scale preparation of ethylene, e.g. bycracking of naphtha in a steam cracker, gives impure ethylene from whichcatalyst poisons which adversely affect the performance ofpolymerization catalysts such as organoaluminum Ziegler-Natta catalystsor chromium-containing Phillips catalysts have to be removed(Industrielle organische Chemie, K. WeiBermel and H.-J. Arpe, VerlagChemie, 1976, pages 57, 58, 59, 65, 66, and Ziegler-Natta Catalysts andPolymerisations, J. Boor, Academic Press 1979, pages 1, 2, 280 to 285).

[0003] Petrochemical Technology Quarterly (PTQ), pages 103 to 107 (1997)discloses Cu/ZnO catalysts for the purification of feedstock forpolymerizations. The performance of these catalysts at low temperaturesis in need of improvement and they are sensitive to acetyleneimpurities.

[0004] It is an object of the present invention to remedy theabovementioned disadvantages.

[0005] We have found that this object is achieved by new and improvedcatalysts for the purification of ethylene comprising copper and zincand, if desired, one or more promoters and supports and produced byprecipitation, drying, calcination and pressing, with or withoutaddition of additives, wherein the pressed catalyst particles aresubjected to further calcination at from 300 to 700° C.

[0006] The catalysts of the present invention can be produced, forexample, as follows:

[0007] Using conventional methods, nitrate solutions of copper and zinccan be precipitated, for example by means of sodium hydrogen carbonatesolution at from 20 to 80° C., preferably from 25 to 700° C.,particularly preferably from 30 to 600° C., in particular from 40 to 55°C., and these precipitates can be mixed with an Al₂O₃ suspension,washed, slurried and spray dried, calcined and shaped (with or withoutaddition of additives such as graphite, talc, stearates, Walocel,starch, boron trifluoride).

[0008] The shaped catalysts obtained in this way are subjected to anafter-treatment by calcination at from 300 to 700° C., preferably from350 to 650° C., particularly preferably from 400 to 600° C., inparticular from 450 to 580° C., for generally from 0.5 to 10 hours,preferably from 1 to 3 hours, particularly preferably from 1 to 2 hours,in particular from 1 to 1.5 hours. In a particularly preferredembodiment, the temperature increases during the residence time.

[0009] The novel catalysts obtained in this way generally have a BETsurface area of from 10 to 100 m²/g, preferably from 30 to 90 m²/g,particularly preferably from 40 to 80 m²/g, in particular from 50 to 75m²/g.

[0010] In the production of the catalysts of the present invention, theyare generally obtained in “oxidized” form, i.e. the copper is present inthe catalyst in the form of copper oxide. These catalysts of theinvention can be converted into their “reduced” form by means ofhydrogen, preferably in a hydrogen atmosphere at from 80 to 180° C.,preferably from 100 to 160° C., particularly preferably from 120 to 140°C., and a pressure of from 1 to 50 bar, so that the copper in them is atleast partly present in metallic form. In a particular embodiment, the“reduced” form of the catalysts can also be obtained in situ, i.e. bymixing sufficient amounts of hydrogen into the ethylene stream to bepurified.

[0011] The composition of the catalysts in “oxidized” form can be variedwithin a wide range. In general, suitable catalysts comprise from 30 to50% by weight, preferably from 35 to 45% by weight, particularlypreferably from 40 to 45% by weight, of CuO, from 30 to 50% by weight,preferably from 35 to 45% by weight, particularly preferably from 40 to45% by weight, of ZnO, from 5 to 40% by weight, preferably from 10 to30% by weight, particularly preferably from 20 to 30% by weight, ofAl₂O₃, SiO₂, TiO₂, MgO, iron oxides or mixtures thereof and from 0 to 5%by weight, preferably from 0 to 2% by weight, particularly preferablyfrom 0 to 1% by weight, of promoters, and preferably consist of theseexcept for trace components which are associated with the abovementionedcomponents.

[0012] Suitable promoters are potassium, sodium, manganese, chromium,cobalt, tungsten, molybdenum, nickel, iron, magnesium, calcium ormixtures thereof, preferably potassium, manganese, chromium, molybdenumor mixtures thereof, particularly preferably potassium, chromium,molybdenum or mixtures thereof.

[0013] The size and shape of the catalysts of the invention can bechosen freely, for example tablets, rings, stars, wagon wheels,extrudates such as cylinders or pellets; preference is given to annulartablets or tablets.

[0014] The purification of ethylene using the catalysts of the presentinvention can be carried out as follows:

[0015] The ethylene to be purified can, in a two-stage process, bereacted

[0016] a) in the presence of hydrogen over the catalysts of the presentinvention in the reduced state at from 70 to 110° C., preferably from 75to 100° C., particularly preferably from 80 to 95° C., and a pressure offrom 5 to 80 bar, preferably from 10 to 70 bar, particularly preferablyfrom 20 to 60 bar, and subsequently

[0017] b) over the catalysts of the present invention in the oxidizedstate at from 70 to 110° C., preferably from 75 to 100° C., particularlypreferably from 80 to 95° C., and a pressure of from 5 to 80 bar,preferably from 10 to 70 bar, particularly preferably from 20 to 60 bar.

[0018] The catalysts of the present invention have a higher resistanceto acetylenes than catalysts which have not undergone an after-treatmentaccording to the invention by subsequent calcination of the shapedbodies. The catalysts of the present invention can be operated at acontent of acetylenes of up to 200 ppm in the ethylene to be purified.

[0019] This two-stage process can be preceded by a hydrogenation step inwhich the ethylene to be purified is passed together with a sufficientamount of hydrogen over a hydrogenation catalyst, e.g. a noble metalhydrogenation catalyst, for example 0.3% by weight of Pd on an Al₂O₃support. This is generally appropriate when large amounts of acetylenes,i.e. amounts of more than 200 ppm, are present in the ethylene to bepurified.

EXAMPLES Example 1

[0020] Production of the Comparative Catalyst

[0021] A mixed metal nitrate solution is prepared from 54% strengthnitric acid, copper metal and zinc oxide, with the Cu/Zn ratio having tobe 100:103. Using this solution, a precipitation with 20% strengthsodium carbonate solution is carried out in an aluminum hydroxideslurry. The precipitate slurry produced in this way is subsequentlyfiltered in a filter press and washed. After filtration and washing ofthe filtercake, the filtercake was slurried, filtered again and washed[electrical conductivity: less than 150 microsiemens; nitrate content:less than 25 ppm]. The filtercake was slurried with water to produce a20% strength by weight suspension and this was spray dried to give apowder which was calcined for 1 hour at 525° C. in a rotary tube. [Theloss on ignition determined by the measurement method GV 900 (loss onignition at 900° C.) was 12% by weight.] The powder obtained in this waywas mixed with 1% by weight of graphite and pressed to form cylindricaltablets having a diameter of 5 mm and a thickness of 3 mm. Thesecontained 40% by weight of CuO, 40% by weight of ZnO, 19.9% by weight ofAl₂O₃ and 0.1% by weight of K₂O as promoter. The bulk density was 1.2kg/l, the porosity was 0.3 ml/g, and the BET surface area was 125 m²/g.

Example 2

[0022] Production of the Catalyst of the Present Invention

[0023] The conventional catalyst obtained as described above wascalcined in a rotary tube at 490° C. in the inlet zone and 550° C. inthe outlet zone, i.e. at a temperature which increased during theresidence time, for 1.2 hours. The bulk density was 1.24 kg/l, theporosity was 0.34 ml/g, and the BET surface area was 64 m²/g.

Example 3

[0024] Preparation of Carbon Dioxide from Carbon Monoxide

[0025] A gas mixture comprising 1125 standard 1/h of nitrogen and 0.1%by volume of carbon monoxide was passed through a test apparatuscomprising an adiabatically operated reactor containing a catalystcharge of 450 ml at a space velocity of 2500 standard liters of gas perliter of catalyst and hour at from 90 to 120° C. At the outlet, theremaining unreacted carbon monoxide was measured. The conversion and thetemperature required are a measure of the effectiveness.

[0026] The results are reported below.

[0027] Catalyst as Described in Example 1

[0028] At a reaction temperature of 91° C., relatively no oxidation tookplace; all the CO broke through, i.e. it was found again at the outletof the test apparatus. At 120° C., the conversion was greater than 99%only during the first minutes; after 15 minutes, 90 ppm of CO werepresent in the tailgas (conversion: 91%), while after 10 hours largeamounts broke through and the content was 360 ppm (conversion: 36%).

[0029] Catalyst as Described in Example 2

[0030] At a reaction temperature of 91° C., the gas at the outlet of thetest apparatus contained only 9 ppm of CO both after 10 hours and after18 hours. The conversion was thus 99.1% after both 10 hours and 18hours.

1. A catalyst for the purification of ethylene, comprising copper and zinc and, if desired, one or more promoters and supports and produced by precipitation, drying, calcination and pressing, with or without addition of additives, wherein the pressed catalyst particles are subjected to further calcination at from 300 to 700° C.
 2. A catalyst for the purification of ethylene, consisting of copper and zinc, if desired partly in oxidic form, and if desired, one or more promoters and supports and produced by precipitation, drying, calcination and pressing, with or without addition of additives, wherein the pressed catalyst particles are subjected to further calcination at from 300 to 700° C.
 3. A catalyst as claimed in claim 1 or 2 which has a BET surface area of from 10 to 100 m²/g.
 4. A process for the purification of ethylene using a catalyst as claimed in any of claims 1 to 3, which comprises a) operating the catalyst in the reduced state in the presence of hydrogen at from 70 to 110° C. and a pressure of from 5 to 80 bar and subsequently b) in the oxidized state at from 70 to 110° C. and a pressure of from 5 to 80 bar.
 5. The use of a catalyst as claimed in any of claims 1 to 3 for the purification of ethylene.
 6. The use of a catalyst as claimed in any of claims 1 to 3 for the purification of ethylene at from 70 to 110° C. 